1. Field of the Invention
This invention is related to powder coating compositions and in particular, to a thermosetting polymer powder coating composition.
2. Description of the Prior Art
To curb pollution caused by conventional solvent based coating systems, the automobile and truck manufacturing industry intends to utilize powder coating compositions. However, the industry demands that these powder coating compositions be of a high quality.
Thermosetting powder coating compositions of polyester resins cross-linked with polyisocyanates are well known in the art as shown in British Pat. No. 1,265,634, published Mar. 1, 1972 and British Pat. No. 1,320,657, published June 20, 1973. In general, these polyester powder coatings do not have the high level of outdoor durability that is required for exterior use on automobile and truck bodies. Powders of acrylic polymers cross-linked with aromatic polyisocyanates are known as shown in Labana U.S. Pat. No. 3,676,405, but coatings from these powders would have poor exterior durability. In addition, the thermosetting powders heretofore known in the art have a poor appearance caused by inadequate flow of the finish during baking. The above defects make the compositions unacceptable for an exterior finish for automobile and truck bodies.